Lubricated screw



Patented @et Q, i934 1,976,305 LUBRICA'IED SCREW Paul G. Swanson andErik Harold Ericsson, Rockford, Ill., assignors to lElco Tool & ScrewCorporation, Rockford, lll., a corporation of Illinois Application `lune26, 1933, Serial No. 677,537

4 Claims.

The invention pertains to screws, adapted for entry into wood or similarsubstance, and has more particular reference to metallic wood screws ofthis type, having a coating of a lubricating material applied theretofor the purpose of facilitating the operation of driving the screws intowood or other hard substance.

It is of course, well known that by applying a lubricant such as beeswaxto the threaded portion of a screw, a substantial reduction in thedriving force required may be effected. In fact, some large users ofscrews such as automobile body manufacturers have adoptedY the practiceof dipping the screws in molten beeswax for this purpose. This practice,however, is expensive, and further, it results in the application of aheavy coating of the wax with an attendant gumrny and sticky surface towhich dirt and grit will adhere, so that it is capable of employmentonly by the users of the screws.

The primary object of our invention is to provide as a new article ofmanufacture, a wood screw or the like having an applied coating of alubricating material in the form of a thin lm firmly adhering to themetallic surface of the screw and of such character as to facilitatesubstantially the driving operation, but at the same time avoiding asticky and gummy surface, thereby rendering the production of suchscrews for general distribution entirely practicable.

A further object is to provide a screw having a relatively hard andsmooth surface coating which is substantially incapable of detection bythe ordinary senses of touch and sight, but nevertheless effective to ahigh degree in facilitating the passage of the screw into the work andthis without reducing its holding power.

Still another object is to provide as a new article of commerce apractical lubricated screw capable of being produced at a cost notmaterially greater than the cost of ordinary screws.

In the accompanying drawing we have shown a side elevational view of ascrew embodying our invention.

While the invention is not limited to screws of any particular kind orcharacter, we have shown in the drawing a conventional wood screw havinga body with a threaded lower end portion 4 and an unthreaded upper endportion 5. The latter carries a head 6 with the usual driving kerf 7 cutin its upper surface. To the outer surface of the screw is applied acoating of a liquid lubricating material providing an extremely thin lmfirmly adhering to the metallic surface of the screw and presenting ahard dry finish at normal temperatures. For best results this materialis applied to the screw in a quantity so small as to be substantiallyimperceptible. In the drawing it is designated by the legend ThinCoating of Lubricant.

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Preferably, the coating is applied to the entire metallic surface notonly because this is more convenient from the manufacturing standpoint,but because it is found that the coating material serves to protect themetal of the screw against rust or corrosion. While the coating materialis thus applied to the head with its driving kerf 7, this is notobjectionable when the coating is very thin in that the quantity ofmaterial lodging in the kerf is not suicient to cause slippage betweenthe driving bit and the walls of the kerf.

In practice, the coating material is applied by submerging the screwsinto a liquid bath of the desired characteristics. For this purpose, aconvenient quantity of screws is placed in a suitable carrier orhanger., which may be made of wire or the like, and upon the removal ofthe screws from the bath they are subjected to centrifugal action whilestill in the carrier. Preferably, heat is applied to the solution in asu'icient quantity to maintain a high degree of fluidity, so that whenthe screws are subjected to the aforesaid centrifugal action, the amountof material adhering to the metallic surface is so small as to bepractically imperceptible.

It will be observed that by applying the coating to the screws in themanner above set forth, the entire surface thereof becomes coated. Thisis advantageous because it permits of the rapid treatment of a largenumber of screws simultaneously. Moreover, when the screws are submergedin a heated solution, the heat of the material is imparted to the screwsso that when the latter are withdrawn from the bath the cooling of thematerial is suiciently retarded to insure removal of all but a verything coating.

It will of course be understood that the particular ingredients employedin the solution may be varied within the spirit and scope of ourinvention. A satisfactory coating bath may be obtained by using one partof the following concentrated solution with four parts by ,volume ofwater:

Per cent by weight Hard soap (preferably in flake form) 2.5 Beeswax 12.5Stearic acid 25.0 Potash 5.0 Water 55.0

When the above solution is cold, it takes the form of a relatively thickemulsion, but by the application of heat its viscosity may be reduced tothe desired degree to permit of the application of a thin coating. Thestearic acid and potash combine to form a soft soap which, like beeswax,is an excellent lubricantfor facilitating the driving of screws intowood and like material. This soft soap and beeswax will mix or combinein any proportion.- xHowever, if the amount of beeswax employed ismaterially increased, a sticky surface results. Through the use of asmall amount of hard soap, a. harder finish is obtained in thecomposition.

It is of the essence of our invention that the lubricating material beapplied in the form of a liquid so as to form a thin film, and that itbe of a character such as to insure that this film shall adhere firmlyto the metallic surface of the screw. Also it is important that thecoating material shall present a dry hard finish at normal temperatures,which does not become sticky in warm weather, does' not detract from theappearance of the screw and offers no objection on account of a tendencyfor dust and grit to adhere thereto. Moreover, due to the character ofthe material and the method of applying the same, the cost ofmanufacture is not increased materially over ordinary screws.

In the use of the improved screw, it has been found that notwithstandingthe application of an extremely thin substantially imperceptiblecoating, the operation of driving the screws into wood or othersubstance is substantiallyn facilitated. Consequently, substantiallyless force is required for the driving operation. In this connection,tests have shown a reduction of from one-half to two-thirds of thedriving force required as compared to ordinary screws. Moreover, wherethe screws are driven by power actuated screw driving tools into hardwood, as in the case of automobile body manufacture, a large saving iseffected due to the substantial elimination of breakage of the screws.Finally, in the driving operation, the heat of friction developedbetween the screw and the work apparently produces a melting 4of thecoating material which subsequently hardens, thus serving to set or bindthe screw in position.

We claim as our invention:

screw having a coating of a lubricating material in the form of a thinfilm firmly adhering to the entire metallic surface of the screw andapplied uniformly to such surface in a quantity so small as to besubstantially imperceptible, said coating presenting at normaltemperatures a hard dry finish to avoid the adherence of grit.

2. As a new article of manufacture, a metallic,

screw having a coating of a lubricating material in the form of a thinfilm firmly adhering to the surface of the screw body substantiallythroughout the length thereof and applied uniformly to such surface in aquantity so small as to be substantially imperciptible, said coatingmaterial presenting a hard dry surface at normal temperatures to avoidthe adherence of grit.

3. As a new article of manufacture, a metallic screw having an extremelythin coating of a lubricating material applied to the screw body over asubstantial portion of its length, said coating material being in theform of a film firmly adhering to the metallic surface and presenting ahard dry surface at normal temperatures to avoid the adherence of grit.

4. As a new article of manufacture, a metallic screw-having a coating ofa lubricating material in the form of a thin film firmly adhering to thesurface of the screw body substantially throughout the length thereofbut applied inl a quantity so small as to be substantiallyimperceptible, said coating material presenting a hard dry surface atnormal temperatures and comprising a small amount of beeswax combinedwith a relatively larger amount of soap.

